Bearing device

ABSTRACT

In a bearing device in which a free end of a shaft body to which a rolling bearing is mounted is bent outward in its radial direction into a shape to be pushed against an end face of an inner ring of the rolling bearing so as to prevent the rolling bearing from falling out, a raceway surface of the inner ring of the rolling bearing is subjected to hardening treatment, and another portion of the inner ring is made of raw material which is not hardened. With this arrangement, the caulked portion formed by the caulking plastically deforms the relatively soft inner peripheral corner of the inner ring and as a result, the caulked portion and the inner peripheral corner are adhered to each other strongly.

This application is a division of Ser. No. 09/799,270 now U.S. Pat. No.6,619,852 filed Mar. 5, 2001.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a bearing device such as a hub unit fora vehicle comprising a shaft and a bearing and a rolling bearing mountedto the shaft body.

2. Description of the Related Art

Referring to FIG. 7, in a conventional hub unit, a double row angularcontact ball bearing 82 with vertex of contact angles outside of bearingis fitted and mounted around a shaft portion 81 of a hub wheel 80. Afree end of the shaft portion 81 is bent outward in a radial directionby rolling-caulking. The bent caulked portion 85 pushes an outer endface of an inner ring 84 of the bearing 82. With this pushing operation,the bearing 82 is fixed to the hub wheel 80 to prevent the bearing 82from falling out from the hub wheel 80.

Before the free end of the shaft portion 81 is caulked, the free end hasa shape of a cylindrical portion. This cylindrical portion isrolling-caulked using a caulking jig. With this operation, thecylindrical portion of the shaft portion 81 is bent outward in theradial direction to form the caulked portion 85 so that the inner ring84 is prevented from falling out.

In such a hub unit, an entire outer surface of the inner ring 84 of thebearing 82 is subjected to hardening treatment. Therefore, in order toenhance a resisting force against the falling-out phenomenon of thebearing 82, it is necessary to set a caulking load stronger.

On the other hand, if the caulking load is excessively strong, a racewaysurface of the inner ring 84 is affected and there is an adversepossibility that rolling characteristics of the bearing 82 isdeteriorated. Therefore, it is necessary to set the caulking loadappropriately.

SUMMARY OF THE INVENTION

Therefore, it is a main object of the present invention to provide abearing device capable of appropriately setting a caulking load suchthat a raceway surface of an inner ring is not affected while afalling-out resistance of a bearing can be strengthened.

Other objects, features and advantages of the present invention will beapparent from the following description.

A bearing device of the present invention comprises a shaft body and arolling bearing mounted around the shaft body, wherein the shaft body isprovided at its free end with a caulked portion. The caulked portion isbent outward in a radial direction to push an end face of an inner ringof the rolling bearing, thereby preventing the rolling bearing fromfalling out. A raceway surface of the inner ring of the rolling bearingis subjected to hardening treatments and other portion of the inner ringis made of raw material which is not hardened.

According to such a structure, the portion of the inner ring of therolling bearing other than the raceway surface can be made of rawmaterial. Therefore, the caulked portion formed by the caulkingplastically deforms the relatively soft inner peripheral corner of theinner ring and as a result, the caulked portion and the end face of theinner ring are adhered to each other strongly without adverselyaffecting the raceway surface of the inner ring.

In the invention, preferably, the inner ring is made of high-carbonchromium bearing steel or carbon steel for machine structural use asbase material, and its raceway surface is subjected to hardeningtreatment by induction hardening. The raw material portion of the innerring is prevented from being excessively deformed by a caulking load atthe time of caulking so that a stable structure can be obtained.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other objects as well as advantages of the invention willbecome clear by the following description of preferred embodiments ofthe invention with reference to the accompanying drawings, wherein:

FIG. 1 is a vertical sectional side view of a hub unit before caulkingaccording to a preferred embodiment of the present invention;

FIG. 2 corresponds to FIG. 1 and is a vertical sectional side view ofthe hub unit after caulking;

FIG. 3 is an explanatory view of rolling caulking with respect to thehub unit;

FIG. 4 is a vertical sectional side view of a hub unit according toanother preferred embodiment of the invention;

FIG. 5(A) is a side view of an essential portion of a hub unit beforecaulking according to another preferred embodiment of the invention;

FIG. 5(B) corresponds to FIG. 5(A), and is a side view of an essentialportion of a hub unit which is being caulked according to anotherpreferred embodiment of the invention;

FIG. 5(C) corresponds to FIG. 5(A), and is a side view of an essentialportion of a hub unit after caulking according to another preferredembodiment of the invention;

FIG. 6 is an explanatory view for FIGS. 5(A) (B) (C), and shows hardnessin each peripheral region of an inner ring; and

FIG. 7 is a vertical sectional side view of a conventional hub unit.

In all these figures, like components are indicated by the samenumerals.

DETAILED DESCRIPTION OF THE INVENTION

Hub units for a vehicle in accordance with preferred embodiments of thepresent invention will be explained with reference to the drawingsbelow.

In a hub unit according to a preferred embodiment of the presentinvention shown in FIGS. 1 and 2, a numeral 1 indicates a hub wheel as ashaft body, a numeral 2 indicates a double row angular contact ballbearing with vertex of contact angles outside of bearing, and a numeral3 indicates a caulked portion.

The hub wheel 1 includes an annular plate 11 and a shaft portion 12.

A wheel (not shown) is mounted to the annular plate 11.

The shaft portion 12 includes an outer peripheral surface 12 b which iscontinuously formed on the annular plate 11. A portion of the outerperipheral surface 12 b closer to the annular plate 11 is larger indiameter. The annular plate 11 also includes an outer peripheral surface12 a which is continuously formed on the large-diameter outer peripheralsurface 12 b. The outer peripheral surface 12 a is smaller than theouter peripheral surface 12 b in diameter. A free end of the shaftportion 12 is formed into a cylindrical portion 12 c before it iscaulked, and after it is caulked, the free end becomes the caulkedportion 3 for fixing the bearing 2.

The bearing 2 is fitted around the shaft portion 12 of the hub wheel 1.

The bearing 2 includes a first inner ring 21 which is fitted around thesmall-diameter outer peripheral surface 12 a of the shaft portion 12 andwhich has a single raceway groove, a second inner ring which comprisesthe large-diameter outer peripheral surface 12 b of the shaft portion 12of the hub wheel 1 and which has a single raceway groove, a single outerring 22 having double rows of raceway grooves respectively correspondingto the raceway grooves of both the inner rings, a plurality of balls 23arranged in two rows between the raceway grooves of both the inner ringsand the raceway grooves of the outer ring 22, and two crown-likeretainers 24 and 25 for respectively retaining the balls 23 in the rows.

The outer ring 22 is provided at its outer periphery with a flange 26directed outward in the radial direction for mounting the hub unit to anaxle case (not shown) or the like non-rotatably.

The inner ring 21 of the bearing 2 is made of high-carbon chromiumbearing steel (JIS specification SUJ-2) or carbon steel for machinestructural use as base material, and its raceway surface 21 b out of itsouter surface is subjected to hardening by induction hardening only inFIGS. 1 and 2, the hardened portion is shown with cross-hatching.

As shown in FIGS. 5(A), 5(B), 5(C) a inner peripheral corner 21 a of theinner ring 21 is roundly chamfered with a radius of curvature r. Thechamfering shape may be tapered shape. However, if the inner peripheralcorner 21 a is chamfered roundly, adhesion of the caulked portion 3 withrespect to the chamfering is enhanced, and a caulking load isexcellently applied.

The manner for forming the caulked portion 3 will be explained withreference to FIG. 3. In FIG. 3, the free end side of the shaft portion12 is shown such that its cylindrical portion 12 c before it is caulkedis shown with a phantom line, and the caulked portion 3 after it iscaulked is shown with a solid line.

First, the inner ring 21 is press-fitted around the small-diameter outerperipheral surface 12 a of the shaft portion 12 of the hub wheel 1.Then, the cylindrical portion 12 c of the shaft portion 12 isroll-caulked using a caulking jig 90. At that time, a tip end of thecaulking jig 90 is set on the cylindrical portion 12 c of the shaftportion 12, and the caulking jig 90 is rolled around a perpendicularline M. With this operation, the cylindrical portion 12 c is bentoutward in the radial direction to form the caulked portion 3. The innerring 21 is prevented from falling out by means of the caulked portion 3.

As described above, since the raceway surface 21 b of the inner ring 21is subjected to the hardening treatment and other portion of the innerring 21 is left as raw material which is not hardened. Therefore, thecaulked portion 3 formed by the caulking plastically deforms therelatively soft inner peripheral corner 21 a of the inner ring 21 and asa result, the caulked portion 3 and the inner peripheral corner 21 a areadhered to each other strongly.

Thus, even if the caulking load is not set so strong at the time ofcaulking, a sufficient strength can be secured, and distortion is notgenerated on the raceway surface 21 b of the inner ring 21 in thecaulking process.

As explained above, the entire outer surface of the inner ring 21against which the caulked portion 3 pushes is not hardened, and only theraceway surface 21 b of the inner ring 21 is hardened. Therefore, it ispossible to strongly push the caulked portion 3 against the inner ring21 and adhere both of them as described above, thereby the falling-outresistant force can be enhanced by the caulked portion 3, andreliability is enhanced.

Although the hub unit especially for the driven wheel for the vehicle isdescribed as above, a hub unit for a driving wheel as shown in FIG. 4 ora guide roller of a slide door such for an automobile and other generalbearing may be used. In FIG. 4, a drive shaft 4 is spline-fitted into ahollow portion of the hub wheel 1 and connected thereto using a nut 5.

Another preferred embodiment of the present invention applied to the hubunit shown in FIG. 4 will be explained with reference to FIGS. 5 and 6.

The shaft portion 12 of the hub wheel 1 in this hub unit is of a hollowstructure. A shaft end of the shaft portion 12 is the cylindricalportion 12 c before it is caulked.

In the inner peripheral corner 21 a of the inner ring 21 of the bearing2, a point of intersection between a line from the center O in theradial direction and the inner peripheral corner 21 a is defined as achamfering-starting point 21 a 1. The chamfering-starting point 21 a 1is a bending-starting point when the cylindrical portion 12 c is bentoutward in the radial direction. A numeral 21 a 2 denotes achamfering-ending point.

The cylindrical portion 12 c is bent outward in the radial direction.The cylindrical portion 12 c is bent from 0° as shown in FIG. 5(A) to45° shown in FIG. 5(B), and then bent further as shown in FIG. 5(C).

At that time, when the bending angle is 45° as shown in FIG. 5(B), aperipheral region 30 of the inner peripheral corner 21 a of the innerring 21 is set such that a depth H1 from a contact point B between thecylindrical portion 12 c and the inner peripheral corner 21 a is equalto or greater than the radius of curvature r.

The reason why the depth H1 of the peripheral region 30 is set as aboveis that a range for effectively absorbing a caulking load need be widerthan both the chamfering-starting point 21 a 1 and the chamfering-endingpoint 21 a 2.

This peripheral region 30 is a fan-like region having a radius centeredon the contact point B as shown with hatching. Vickers hardness Hv inthis peripheral region 30 is set 400 or less at a surface layer thereofbecause the distortion deformation force applied at the time of caulkingis plastically absorbed with this hardness. Here, the surface layer is alayer located in a depth of about 1 mm from a surface of the peripheralregion 30.

The reason why the Vickers hardness of the peripheral region 30 isdefined at the surface layer is that since the hardness may be loweredby induction heating and the hardness of the surface of the peripheralregion 30 becomes lower than that of the inside thereof.

Here, a reference numeral 31 represents a peripheral region of theraceway surface 21 b of the inner ring 21. The peripheral region 31 is aregion shown with cross-hatching and has a depth H0 in a direction ofcontact angle from the raceway surface 21 b of the inner ring 21. TheVickers hardness Hv of the peripheral region 31 is 500 or higher, andespecially, the hardness of the raceway surface 21 b is about 800. Inthis case, the depth H0 of the peripheral region 31 with respect to amaximum shearing stress depth Z0 is H0≧8·Z0.

This will be explained with reference to FIG. 6. A vertical axis in FIG.6 shows the Vickers hardness Hv, and a horizontal axis shows the depthof the peripheral regions 30 and 31.

In FIG. 6, a symbol A indicates a graphical position corresponding to adepth on the raceway surface 21 b in the peripheral region 31, z0indicates a graphical position corresponding to the maximum shearingstress depth z0, and H0 indicates a graphical position corresponding toa maximum depth of the peripheral region 31 located at a position of 8times or more of the maximum shearing stress depth z0. The Vickershardness Hv in the peripheral region 31 is 500 or more.

The reason why the maximum depth H0 of the peripheral region 31 is setas above is that the life of the rolling bearing is affected by shearingstress. The above value of the depth H0 has been experimentallydetermined.

The reason why the Vickers hardness Hv of the peripheral region 30 isset 400 or less, and the Vickers hardness Hv of the peripheral region 31is set 500 or greater is that these values are necessary in terms oflife in the case of the peripheral region 31 and in terms of loadabsorption in the case of the peripheral region 30.

A symbol B indicates a graphical position corresponding to a depth onthe inner peripheral corner 21 a in the peripheral region 30, rindicates a position corresponding to a depth of radius r from thecorner 21 a, and H1 indicates a position corresponding to a maximumdepth of the peripheral region 30.

In order to improve abrasion resistance and strength of the racewaysurface 21 b, such entire inner ring 21 including the peripheral regions30 and 31 is hardened by heat treatment such as quenching, and theperipheral region 30 is low-hardened by quenching treatment such aslocal induction heating after the heat treatment and thus, the hardnessrelation shown in FIG. 6 is obtained.

According to the above-described structure, in the case of the hub unitof the present embodiment shown in FIGS. 4 to 6, the caulking load atthe time of caulking of the cylindrical portion 12 c of the hub wheel 1is absorbed by plastic deformation of the peripheral region 30 which islow-hardened of the inner ring 21 and as a result, distortion is notgenerated in the raceway surface 21 b of the inner ring 21 in thecaulking process.

While there has been described what is at present considered to bepreferred embodiments of this invention, it will be understood thatvarious modifications may be made therein, and it is intended to coverin the appended claims all such modifications as fall within the truespirit and scope of this invention.

1. A bearing device comprising: a shaft body; and a rolling bearingwhich is mounted around said shaft body, wherein said shaft body isprovided at its free end with a caulked portion, said caulked portionbeing bent outward in a radial direction for pushing an end face of aninner ring of said rolling bearing thereby preventing said rollingbearing from falling out, wherein said inner ring of said rollingbearing is entirely hardened by heat treatment in order to improveabrasion resistance and strength of a raceway surface defined by saidinner ring, and wherein a peripheral region of an inner peripheralcorner of said inner ring is low-hardened by local quenching after saidheat treatment.
 2. A bearing device comprising: a shaft body; and arolling bearing which is mounted around said shaft body, wherein saidshaft body is provided at its free end with a caulked portion, saidcaulked portion being bent outward in a radial direction for pushing anend face of an inner ring of said rolling bearing thereby preventingsaid rolling bearing from falling out, an end surface of said inner ringconstituting a crimp contact portion in contact with said caulkedportion, wherein hardness of a peripheral region of an inner peripheralcorner of said inner ring is set to a value capable of plasticallyabsorbing a load at the time of caulking; and wherein said innerperipheral corner of said inner ring is roundly chamfered with apredetermined radius of curvature, said peripheral region of said innerperipheral corner is set as a region where a depth from said innerperipheral corner is equal to or greater than said predetermined radiusof curvature and wherein a peripheral region of a raceway surface ofsaid inner ring does not overlap, and hardness of said inner peripheralcorner peripheral region is set less than that of at least saidperipheral region of said raceway surface of said inner ring.
 3. Abearing device comprising: a shaft body; and a rolling bearing which ismounted around said shaft body, wherein said shaft body is provided atits free end with a caulked portion, said caulked portion being bentoutward in a radial direction for pushing an end face of an inner ringof said rolling bearing thereby preventing said rolling bearing fromfalling out, an end surface of said inner ring constituting a crimpcontact portion in contact with said caulked portion, wherein hardnessof a peripheral region of an inner peripheral corner of said inner ringis set to a value capable of plastically absorbing a load at the time ofcaulking; wherein said inner peripheral corner of said inner ring isroundly chamfered with a predetermined radius of curvature; and whereinsaid peripheral region of said inner peripheral corner is set as aregion where a depth from said inner peripheral corner is equal to saidpredetermined radius of curvature and a peripheral region of a racewaysurface of said inner ring does not overlap, and hardness of said innerperipheral corner peripheral region is set less than that of at leastsaid peripheral region of said raceway surface of said inner ring.
 4. Abearing device comprising: a shaft body; and a rolling bearing which ismounted around said shaft body, wherein said shaft body is provided atits free end with a caulked portion, said caulked portion being bentoutward in a radial direction for pushing an end face of an inner ringof said rolling bearing thereby preventing said rolling bearing fromfalling out, an end surface of said inner ring constituting a crimpcontact portion in contact with said caulked portion, wherein hardnessof a peripheral region of an inner peripheral corner of said inner ringis set to a value capable of plastically absorbing a load at the time ofcaulking; wherein said inner peripheral corner of said inner ring isroundly chamfered with a predetermined radius of curvature; and whereinsaid peripheral region of said inner peripheral corner is set as aregion where a depth from said inner peripheral corner is greater thansaid predetermined radius of curvature and wherein a peripheral regionof a raceway surface of said inner ring does not overlap, and hardnessof said inner peripheral corner peripheral region is set less than thatof at least said peripheral region of said raceway surface of said innerring.
 5. A bearing device comprising: a shaft body; and a rollingbearing which is mounted around said shaft body, wherein said shaft bodyis provided at its free end with a caulked portion, said caulked portionbeing bent outward in a radial direction for pushing an end face of aninner ring of said rolling bearing thereby preventing said rollingbearing from falling out, an end surface of said inner ring constitutinga crimp contact portion in contact with said caulked portion, whereinhardness of a peripheral region of an inner peripheral corner of saidinner ring is set to a value capable of plastically absorbing a load atthe time of caulking; wherein said inner ring has a variable hardness;and wherein said peripheral region of said inner peripheral corner ofsaid inner ring has a Vickers hardness of 400 or less at a surface layerand a peripheral region of a raceway surface defined by said inner ringhas a Vickers hardness of 500 or more.
 6. A bearing device comprising: ashaft body; and a rolling bearing which is mounted around said shaftbody, wherein said shaft body is provided at its free end with a caulkedportion, said caulked portion being bent outward in a radial directionfor pushing an end face of an inner ring of said rolling bearing therebypreventing said rolling bearing from falling out, wherein hardness of aperipheral region of an inner peripheral corner of said inner ring isset to a value capable of plastically absorbing a load at the time ofcaulking, wherein said inner peripheral corner of said inner ring isroundly chamfered with a predetermined radius of curvature, saidperipheral region of said inner peripheral corner is set as a regionwhere a depth from said inner peripheral corner is equal to or greaterthan said predetermined radius of curvature, and wherein a peripheralregion of a raceway surface of said inner ring does not overlap, andhardness of said inner peripheral corner peripheral region is set lessthan that of at least said peripheral region of said raceway surface ofsaid inner ring.